Project Summary: Allergic reactions are elicited by the allergen-mediated-clustering of the immunoglobulin E (IgE) antibodies on the surface of mast cells, which is ?the key event? in initiation of the systemic reaction. Allergic diseases are increasing health concerns in developed nations. Depending on the severity of the allergic reaction, the results can vary from a simple itch to anaphylactic shock, which results in 1,500 deaths each year in the US. There are no cures for allergies, and current therapies focus on treatment of acute symptoms or chronic immune suppression. Even with the most restricted diets, accidental exposure is very frequent for food allergies, putting patients at risk for life threatening anaphylaxis. Thus, there is a need for more effective, alternative treatments for IgE-mediated allergic responses. The objective of this application is to develop allergen-specific IgE inhibitors (cHBI: covalent heterobivalent inhibitor) that target allergen-binding IgE, and prevent it from recognizing the allergen. This approach inhibits the allergic reaction before it starts with specific targeting but without broad immune suppression. Naturally occurring allergens are typically complex, structurally heterogenous proteins with multiple allergy-inducing epitopes. Historically it has been a challenge to identify contributions from individual allergen epitopes to the overall allergic reaction. During the previous funding cycle, we addressed this problem by developing a multicomponent epitope presentation platform that we named nanoallergens. Using nanoallergen screening, we can study the immunogenicity of individual allergen epitopes, and identify immunodominant epitopes. Using the identified immunodominant epitope, we synthesize cHBI inhibitors that mimic the epitope and block the IgE antibodies that recognize the specific epitope. This method inhibits the IgE from recognizing the allergen when it enters the system and prevents the initiation of the allergic reaction. We have recently demonstrated that using a cocktail of cHBIs, we can block peanut allergic reactions using patient samples in an in vitro cellular degranulation method. In the current application, we will evaluate the peanut allergy inhibition in vivo using a humanized mice model. Simultaneously, we will exploit the potential of the cHBI as a platform to block other allergens including shellfish, dust mite and hazelnut. The proposed work is innovative and significant because it (i) offers a novel molecular design approach to inhibit ?the key event? triggering an allergic response with potential long-term clinical applications in food, environmental and drug allergies, (ii) it does so without any non-specific suppression of immune system components, and (iii) develops a much needed, physiologically relevant, easily adjustable and reproducible platform (nanoallergens), which will be used in identifying immunodominant public allergen epitopes and their relative significance during degranulation responses. Lastly, this application has high potential impact because cHBI has the potential for translation to the clinic.